The technical field is microelectronic devices and methods for producing same.
Inkjet printers are commonly used to produce text and images on a variety of media such as paper, transparencies and labels, for example. A typical inkjet printer uses a carriage that holds one or more ink cartridges. The ink that is to be printed on the media is forced through small holes in a thermal inkjet chip to produce the desired text or image. Thermal inkjet chips are small crystal structures that are placed in a larger substrate to provide the desired array of inkjet printing nozzles.
To ensure accurate rendition of text and images, alignment of the thermal inkjet chips and the substrate is a critical design feature. Great care and precision must be used to make sure that the thermal inkjet chips are precisely aligned, thereby causing great expense and time in producing the thermal inkjet printer printheads. In particular, expensive precision tooling is required to align the printheads through the substrate. Second, a mismatch between a coefficient expansion for the printhead and the substrate can result in thermal induced stress on the interconnect used to electrically connect the substrate to the printheads. Additionally, the mismatch can result in misalignment between the substrate and the printheads. Third, the interconnect, the materials used from the substrate, and adhesive used to attach the printheads to the substrates are subject to failure due to the corrosive effect of ink used in inkjet printers. Fourth, the inkjet pens are sensitive to texture variations caused by waste heat from the printheads. The substrate must have a high thermal conductivity so that the waste heat can be dissipated. If the substrate has a low thermal conductivity, then the waste heat can raise temperatures of the pens, resulting in an increase in the amount of ink volumes dropped by the pens. Subsequently, a temperature differential exists among printheads so that the ink drop volumes can vary depending on their location on the substrate. Ideally, the thermal conductivity of the substrate and the printheads would be identical so that there is no temperature differential between the printheads and the substrate, resulting in consistent ink drop volumes among the printheads.
A self-aligned interconnect significantly reduces manufacturing costs and provides important advantages in a number of specific applications begins with a single crystal substrate. The substrate is machined to accept microelectronic chips at various locations (openings) along the substrate. Corresponding chips are constructed to precisely fit the openings in the crystal substrate. To ensure precision fit, both the substrate and the chip are etched along the same crystal plane. As a result, the chips can be placed in the openings in the substrate with perfect or nearly perfect alignment in the x and y directions without expensive alignment tools. In effect, the chips and the substrate are self aligned.
In an embodiment, the chips may be thermal inkjet (TIJ) chips that are used to deliver ink in association with an inkjet printer.
Variation in the thickness of the chips, and to a smaller degree, any over etching, may result in variation in the height of the chip in the z direction. However, the assembly process ensures that no skew will occur in the z plane. In the context of printing, inkjet printers are not sensitive to z direction variation as long as the variation is small compared to the printhead to paper spacing.
Electrical interconnects on the chip and the conducting wiring on the silicon substrate are patterned with a matching pitch. As a result, the two parts (chip and substrate) are matched together, and the interconnect wiring, chip and the substrate will be in perfect alignment or near perfect alignment without any alignment effort.
The chips and substrate may be mated together using a glue, adhesive or solder. The adhesive may be used to reduce frictional forces and to provide a tight seal. In a specific application of an inkjet printer, the seal prevents corrosive ink from affecting delicate wiring on the chips and the substrate.